The illustrator, Sarah Walsh, is an American artist who's interests include vintage and magical creatures, which I think you can see in her artwork. The drawings seem to have a period-style to them, as if they're from another era. I'm reminded of Venetian masquerade masks, street parades and booming drums. It really takes you into another world whilst you're colouring, which I love.
There are lots of books in the Just Add Color series, and if the standard of drawings and paper is anything like this one I'll definitely be purchasing the rest. Have a look at my completed pictures!